1 Department of Animal Science, Federal University of Viçosa, Viçosa, Brazil; 2 Department of Preventive Veterinary Medicine, Londrina State University, Londrina, Brazil; 3 Department of Animal Biology, Federal University of Viçosa, Viçosa, Brazil; 4 Department of Immunology, Federal University of Viçosa, Viçosa, Brazil; 5 Department of Preventive Veterinary Medicine and Public Health, Paranaense University, Umuarama, Brazil.
Streptococcosis causes serious economic losses to fish farms every year. A four-week feeding trial was carried out to evaluate arginine (ARG) supplementation in the diet of Nile tilapia (Oreochromis niloticus) fingerlings challenged by Streptococcus agalactiae. Fish were fed with experimental diets containing five levels of supplementation with 1.39%, 1.76%, 1.97%, 2.18% or 2.39% analysed level of ARG. Each diet was randomly distributed in 30 tanks containing 20 fish/tank. After 30 days, no differences were observed in performance parameters, weight gain, daily weight gain, specific growth rate, feed intake or food conversion. After the performance assay, fingerlings were infected with 1.95 × 108 CFU/fish of Streptococcus agalactiae. Mortality was verified daily, and the respiratory burst of leucocytes and nitric oxide production were measured at 0 hr, 24 hr, 7 days and 15 days after infection. The survival rate of the fish is compared using the Kaplan–Meier method, with values of 4.29%, 14.8%, 10.8%, 17.2% and 33.3% for the 1.39, 1.76, 1.97, 2.18 and 2.39 treatments respectively. A reduction in the mortality rate and a boost in the immune responses was observed in all the supplementations of ARG in the diet; however, the best survival rates were obtained in the treatments with 2.39% ARG as well as the most efficient immune responses.
Keywords: arginine supplementation, immunonutrition, Nile tilapia, respiratory burst, streptococcosis, survival rate.
Abstract published in Aquaculture Research 2020;00:1–8. https://doi. org/10.1111/are.14478.